1. Field of the Invention
The present invention relates to a display apparatus that is constituted with pixels arranged in matrix on a substrate and, in particular, to a display apparatus with built-in electronic circuits.
2. Description of the Related Art
Color display apparatuses such as color liquid crystal display apparatuses are used widely. Among the color display apparatuses, especially those of color-filter type using micro-color filters are broadly used mainly for the liquid crystal display apparatuses. An example of the conventional color display apparatus of the color-filter type will be described by referring to the accompanying drawings.
FIG. 16 is a plan view for showing each dot (display unit of a certain color) and layout of color filters within a display area according to the example of the conventional display apparatus. Explanations thereof will be provided hereinafter by referring to this drawing.
In this display apparatus, a color filter of a certain color is provided by corresponding to a single dot. Three colors of R (RED), G (GREEN), and B (BLUE) are used as the colors of the filters. In the lateral direction of the drawing, i.e. in the direction along scanning lines G1, G2, G3, - - - , the color filters of each color are arranged in order of R, G, B, R, G, B, - - - in an orderly manner. In the longitudinal direction, i.e. in the direction along signal lines D1, D2, D3, - - - , color filters of the same color are arranged. Such layout of the color filters is generally referred to as a stripe layout. The stripes are lined in the longitudinal direction in this example, so that this type is referred to as a longitudinal stripe type. Through the three dots lined continuously in the lateral direction by corresponding to the color filters of three colors, it is possible to display all the colors that can be obtained by combining the three fundamental colors. The minimum display unit for displaying all the colors, i.e. the color filters of R, G, B lined in the direction along the scanning line for three dots, is refereed to as one pixel.
Meanwhile, in accordance with the recent technical developments, such display apparatus has been put into practical use, in which various circuits such as a drive circuit and the like, which are conventionally provided outside by LSI and the like formed by a silicon technique, are built-in on a support substrate. An example of such the display apparatus with built-in circuits is a display apparatus formed by a high-temperature polysilicon TFT technique by a high-temperature process using an expensive quartz substrate. Furthermore, a display apparatus having circuits built-in on a glass substrate or the like is put into practical use by a low-temperature polysilicon technique in which a precursor film is formed by a low-temperature process and it is annealed by laser or the like for making it to polycrystalline.
As a specific example, there is an active-matrix type display apparatus disclosed in Japanese Unexamined Patent Publication 2004-046054 (Patent Literature 1). FIG. 17 is a block diagram for showing a display system that comprises a conventional drive circuit integrated type liquid crystal display apparatus shown in FIG. 37 of Patent Literature 1. Explanations thereof will be provided hereinafter by referring to FIG. 17.
In the conventional drive circuit integrated type liquid crystal display apparatus, an active matrix display region 110 where pixels wired in matrix in M rows and N columns are arranged, a scanning circuit for the row direction (scanning line drive circuit or gate line drive circuit) 109, a scanning circuit for the column direction (data line drive circuit) 3504, an analog switch 3505, a level shifter 3503, etc. are integrally formed on a display device substrate 101 by polysilicon TFT.
A controller 113, a memory 111, a digital-analog converter circuit (DAC circuit) 3502, a scanning circuit/data register 3501, and the like are in an integrated circuit chip (IC chip) that is formed on a single-crystal silicon wafer, which is mounted outside the display device substrate 101. An interface circuit 114 is formed on a system-side circuit substrate 103.
Further, among the conventional drive circuit integrated type liquid crystal display apparatus formed by the polysilicon TFT, there are such types in which more complicated circuits such as the DAC circuit and the like are formed integrally. FIG. 18 is a block diagram for showing a display system of a conventional DAC circuit built-in type liquid crystal display apparatus that is shown in FIG. 38 of Patent Literature 1. Explanations thereof will be provided hereinafter by referring to FIG. 18.
Like the drive circuit integrated type liquid crystal display apparatus shown in FIG. 37 of Patent Literature 1 having no built-in DAC circuit, the conventional DAC circuit built-in type liquid crystal display apparatus comprises circuits such as a data register 3507, a latch circuit 105, a DAC circuit 106, a selector circuit 107, a level shifter/timing buffer 108, etc. formed integrally on a display device substrate 101, in addition to the active matrix display region 110 where pixels wired in matrix in M rows and N columns are arranged, the scanning circuit 109 for the row direction, and the scanning circuit 3506 for the column direction.
In this structure, the control IC mounted outside the display device substrate 101 does not include a DAC circuit that uses high voltage. Thus, it can be constituted solely with circuits/devices of low voltage, e.g. the memory 111, the output buffer circuit (D-bit) 112, and the controller 113. As a result, the IC can be fabricated without employing the process for the high-voltage device that is required for generating voltage signals for writing to the liquid crystal. Therefore, the price can be suppressed lower compared to that of the above-described IC on which the DAC is embedded.
Furthermore, the inventors of the present invention has advanced integration of various circuits on a support substrate and invented a method for integrating a memory on the support substrate (Unpublished). Moreover, as a technique for integrating memories, the inventors of the present invention have presented a frame memory on a glass substrate for the first time in the world (SID 05 DIGEST, pp. 1106-1109: Non-Patent Literature 1). FIG. 19 is a block diagram for showing a conventional frame memory on a glass substrate that is shown in FIG. 1 of Non-Patent Literature 1. Explanations thereof will be provided hereinafter by referring to FIG. 19.
In this case, not only the frame memory and the circuit related to the control thereof but also a compression circuit for compressing signals to reduce the size of the frame memory and a decompression circuit for decompressing the compressed signals are provided. The core part of the frame memory is constituted with a memory cell array 121 with a sense amplifier, a row decoder 122, and a column decoder 123. It is possible with the row decoder 122 and the column decoder 123 to access to a specific memory cell within the frame memory. Further, the signal outputted from the memory cell is outputted via the sense amplifier. Such frame memory circuit is formed on a glass substrate 120. FIG. 20 shows the circuits for 1-bit line of the memory cell array 121 with the sense amplifier.
FIG. 20 is a circuit diagram for showing 1-bit line of the conventional memory cell array with a sense amplifier that is shown in FIG. 3 of Non-Patent Literature 1. Explanations thereof will be provided hereinafter by referring to FIG. 20.
At the time of writing, data on a data line 163 is written to a bit line pair that is selected based on a signal from the column decoder. The data on the bit line pair is written to each memory cell 161 of the selected word lines (indicated by W[239], W[118], W[1], W[0] in the drawing). Meanwhile, at the time of readout, the data on the selected word lines is read out to the bit line pair, which is amplified by the sense amplifier 160 and outputted to the output register side.
There are some issues to be overcome in the display apparatuses disclosed in Patent Literature 1 and Non-Patent Literature 1.
The first issue is that the circuits on the support substrate tend to be large-scaled in terms of the layout compared to that of the circuits formed by LSI outside the support substrate. This happens because, with the design rule, the size of the circuit on the support substrate is larger than the circuit of the LSI by the silicon technique. It is because the size of the support substrate used in the display apparatus is generally larger than that of the silicon substrate used in the LSI technique, so that the circuits on the support substrate are more likely to be affected by expansion/contraction of the support substrate itself, or the positioning accuracy by step exposure using a stepper becomes deteriorated, etc.
The second issue is that it is highly difficult to design the layout of the circuits on the support substrate. This is due to the fact that it is difficult to decrease the area occupied especially by the circuits on the signal drive circuit side, in addition to the fact that it requires a contrivance to save the occupied area because the design rule mentioned above is large. This is because the circuits on the signal drive circuit side include not only the scanning circuit but also the analog switch, the level shifter, DAC and the like as described above, so that the circuit structure becomes complicated. Further, as shown in FIG. 16, it is also a reason that the pitch between the signal lines on the signal drive circuit side is narrower than the pitch between the scanning lines on the scanning drive circuit side in the conventional display apparatus. When the pitch in the area for arranging the circuits is narrow, it becomes difficult to draw around the wirings for the input signals necessary for each circuit and the input/output signals between each circuit. In addition, the proportion occupied by the wirings for the signals is increased with respect to the layout area, so that the layout area for the circuits is decreased relatively. As a result, the difficulty of the circuit layout is increased.
The third issue is that the frame (the distance between the end of the display area and the end face of the support substrate) on the signal drive circuit side becomes increased. This is caused because the circuit structure on the signal drive circuit side is complicated and the pitch of the layout is narrow, so that the area occupied by the wirings for the signals is increased. Thus, it needs to increase the length of the circuit area for arranging the necessary circuits.
The fourth issue is that it cannot achieve a highly fine display apparatus. The reason for this is that, as shown in FIG. 25, it is not possible with the longitudinal stripe type to design the layout of the circuits within the circuit pitch determined by the design rule (not possible to arrange the circuits within the circuit pitch), i.e. referring to FIG. 25, it is not possible to design the layout with the longitudinal stripe type by the pixel pitch (141 μm) that correspond to 180 ppi. This issue is different from the aforementioned issues concerning expansion of the frame and an increase in the difficulty of layout. Rather, the issue is that it is not possible to design the layout itself, so the apparatus itself cannot be formed. In order to achieve the layout with this condition, the design rule has to be changed. For changing the design rule, it is necessary to start from a new process development, which is very difficult.
The fifth issue is that the time required for the development is increased. It is because the time required for designing the layout and the like is increased due to the above-described four issues, thereby increasing LT (Lead Time).
The sixth issue is that the cost for the display apparatus is increased. As described above, this is because the time required for the development is increased, thereby mounting up the development cost. Further, another reason for this is that it requires a large number of metal layers since providing the layout is highly difficult. Therefore, the number of processes is drastically increased, thereby increasing TAT (Turn Around Time).
The seventh issue is that an external shape of the display apparatus having a non-rectangular display area becomes largely changed. It is because the frame on the signal line drive circuit side becomes expanded, as mentioned in the description regarding the third issue. For the display apparatus having a non-rectangular display area, it is more effective in terms of the design, if the external shape of the display apparatus is in a shape similar to that of the display area. However, it is difficult with the conventional display apparatus to make the external shape in a similar shape of the display area.